铋改性AZ系镁合金的扩散动力学及非平衡凝固组织调控研究

传统AZ（Mg-Al-Zn）系铸造镁合金高温力学性能欠佳，制约了其在高温服役环境中的应用。铋改性AZ铸造镁合金因其可兼具优良的室温和高温力学性能而备受关注。探明铋改性AZ合金凝固组织演化规律并调控其凝固微结构，是优化其力学性能的有效途径。然而，目前尚缺乏针对铋改性AZ合金凝固组织精准调控的科学依据。据此，本项目以Mg-Al-Zn-Bi四元系为研究对象，拟开展以下研究：1）集成扩散偶实验、理论计算和CALPHAD方法评估镁基体和液相原子移动性参数，并建立体系扩散动力学数据库；2）基于可靠的热、动力学描述及非平衡凝固模拟，构建铋改性AZ合金在不同冷速下的非平衡凝固相转变图；3）采用非平衡凝固相转变图结合凝固过程原位观察实验及多尺度表征，阐明合金成分、冷却速率对凝固微结构演变规律的影响，实现铋改性AZ合金非平衡凝固组织的精准调控。项目的完成将为高性能铋改性AZ系铸造镁合金的高效设计提供科学依据。

Application of the traditional AZ (Mg-Al-Zn) series casting magnesium alloy is limited due to its poor mechanical properties at elevated temperatures. The bismuth-modified AZ series casting magnesium alloy has attracted much attention owing to its excellent mechanical properties both at room-/high- temperatures. It is of great importance to investigate and control the microstructure evolution of the Bi-modified AZ alloys during the solidification process, which will help to improve the mechanical properties. So far, there is no scientific methodology for efficiently controlling the solidification microstructural bismuth-modified to AZ series alloys in the literature. In this proposal, the Mg-Al-Zn-Bi quaternary system is chosen as the research target. The following tasks will be included: 1) by integrating of the diffusion-couple experiments, theoretical predictions and CALPHAD approach, the atomic mobility parameters for both liquid and hcp phases will be firstly obtained, which are used to establish the diffusion kinetic database for Mg-Al-Zn-Bi quaternary system. 2) On basis of the accurate thermodynamic and diffusion information, non-equilibrium solidification simulations for different series of Bi-modified AZ alloys under different cooling rates will be carried out. After that, the non-equilibrium solidification phase transition diagrams of Bi-modified AZ alloys will be constructed by considering all the solidification simulation results. 3) By combining the non-equilibrium solidification phase transition diagrams with in-situ observations of solidification processes as well as multiscale characterization of microstructure, the relationship among compositions, cooling rates and the solidification behaviors can be achieved, which will help to realize the solidification microstructural control for Bi-modified AZ casting alloys. It is highly expected that the completion of this project will provide the scientific basis for the development of high-performance bismuth-modified AZ series casting magnesium alloys.